Comparing trends in BMI and waist circumference.

Area of Science:

• Public Health
• Epidemiology
• Human Physiology

Background:

• Excess body weight is a growing public health concern.
• Central adiposity, indicated by waist circumference (WC), is linked to increased cardiovascular risk.
• Trends in Body Mass Index (BMI) may not fully capture changes in body fat distribution.

Purpose of the Study:

• To determine if BMI and WC are increasing proportionately across population subgroups.
• To examine trends in bodyweight and central adiposity over time.
• To assess the public health implications of changing body composition.

Main Methods:

• Analysis of two US National Health and Nutrition Examination Studies (NHANES) cross-sectional surveys (1988-1994 and 2005-2006).
• Inclusion of 15,349 participants (NHANES III) and 4,176 participants (2005-2006), all aged ≥20 years.
• Statistical adjustments for sex, age, race-ethnicity, and education.

Main Results:

• Between 1988-1994 and 2005-2006, mean BMI increased by 1.8 kg/m² and mean WC by 4.7 cm.
• The increase in WC was greater than explained by BMI increases alone, with an independent average increase of 0.9 cm.
• This independent WC increase was consistent across demographic groups and BMI categories, particularly in younger adults.
• Prevalence of low-risk WC decreased, while increased-risk WC prevalence rose across all BMI categories.

Conclusions:

• Waist circumference is increasing disproportionately to BMI, indicating a shift towards central adiposity.
• BMI trends alone may increasingly underestimate the adverse health consequences of obesity.
• Monitoring both BMI and WC is crucial for accurately assessing cardiovascular risk and public health strategies.